Method for measuring adhesion strength of resin material

ABSTRACT

A method for measuring an adhesion strength of a resin material which is capable of accurately and readily measuring a universal adhesion strength independent of dimensions and shapes of specimen. A delamination portion is partially formed between a resin and an adherend material. Loads in two different directions are applied to an adhering interface such that opposed shear stresses are generated. As a result, a true adhering strength can be obtained from an apparent delamination propagating strength in each case.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display method, a container, acarrying document, an adhesion strength measuring method, and acomposite manufacturing method for resin material (resin composition),and more particularly to a display method, a container, a carryingdocument, an adhesion strength measuring method and a compositemanufacturing method for resin material (resin composition) which iscapable of providing a universal adhesion strength regardless ofdimensions and configuration of adhering specimens, and further to aresin material (resin composition), the adhering reliability of whichcan be easily evaluated.

2. Description Of The Related Art

In resin-molded electronic and electric parts containing insertingcomponents such as resin encapsulated semiconductor devices and resininsulating transformers, the inter-faces between the resin and theinserting components are subjected to high residual stress due to cureshrinkage of the resin and thermal expansion mismatch between the resinand the inserting components.

Further, the internal exothermic action and the harsh heating/coolingoperations increase the thermal stress which sometimes causesdelamination during operations of the components and reliability tests.

Such a delamination at adhering interfaces not only results in corrosionof electric wiring materials and electric insulating degradation, butalso causes a variety of other damages, such as cracking of the resinand wire breaking due to the stress concentration by the delamination.

The evaluation of resin material adhesion strength is therefore acritical issue in assuring the reliability of such resin-moldedcomponents.

Conventional methods for measuring the adhesion strength of resinmaterial apply tensile or shear loads to an adhering specimen, and thendivide the obtained fracture (delamination) loads by the adhesion areaor length as described in IEEE Transactions on Comp., Hybrids, Manuf.Technol., Vol. 14, No. 4 (1991) pp. 809-817 and in Adhesion Technology,Vol. 9, No. 1 (1990) pp. 60-63 and 64-75.

Another method is disclosed in the Proceedings of the 67th Spring AnnualMeeting of the Japan Society of Mechanical Engineers Ser. A (1990), pp.75-77. In this method, a load is applied to an adhering specimen havingpartly formed delaminating portions, and a stress distribution near thedelamination tip, i.e. near the boundary between the delaminatingportion and the adhering portion, at the onset of delaminationpropagation is described by fracture mechanics parameter.

Further, other method is disclosed in the Transactions of the JapanSociety of Mechanical Engineers, Ser. A, Vol. 54, No. 499 (1988) pp.597-603. In this method, a temperature at which delamination takes placedue to a residual stress is measured during cooling process aftermolding an adhering specimen, and a residual stress distribution at thedelamination onset portion at that time is analyzed.

Among aforementioned conventional arts, in the tensile/shear loadsapplying method there is present the residual stress already when theadhering Specimen is made. Therefore, the measurable adhesion strengthwould be nothing more than an apparent adhesion strength, which is asuperimposition of the residual stress on the true adhesion strength.

Particularly in the case of semiconductor transfer molding resin forsemiconductor encapsulation, the adhesion strength is relatively low dueto a mold release agent contained in the resin material for easilyparting from molding die. As a result, the reduction rate of theadhesion strength caused by the residual stress becomes large, such thatthe residual stress sometimes causes by itself the delamination at theinterface.

Even if the adhesion strength measured by such a method is compared toan interface stress obtained by analysis or experiment, the adheringreliability of the resin molded components cannot be evaluated.

Further, the stress at the adhering interface is not uniform, but hassingularity so as to become infinite at the end portions.

All the distributions of the residual stress and the stress caused bythe load application during the adhesion test depend on the dimensions,shapes and materials of the specimens. Accordingly, in such conventionalmethods, as dividing the load by the adhering area on the assumptionthat the stress is uniformly distributed, dividing the load by theadhering length on the assumption that the load acts only on a linealong the delamination front, the resulting adhesion strength depends onthe dimensions, shapes etc. of the specimens, such that no universalmeasured value can be obtained.

If there is no residual stress, it is possible to obtain a universaladhesion strength by a method of describing a stress distribution near asingular point such as delamination tip by use of fracture mechanicsparameters. On the other hand, however, in the case of the residualstress being present, the residual stress distribution must be obtainedby analysis, as in the aforementioned last reference, the Transactionsof the Japan Society of Mechanical Engineers, Ser. A, Vol. 54, No. 499(1988) pp.597-603. The analysis of the residual stress would besometimes quite complicated or difficult to be performed with highaccuracy due to conspicuous temperature dependency of the materialproperties or significant viscoelastic behavior at high temperaturesdepending on the materials of the resin composition.

Further, as in the case of the last reference, if the delamination iscaused only by the residual stress, there would be a disadvantage thatthe adhesion strength may not be freely measured at any desiredtemperatures.

Thus, in the conventional methods, any universal adhesion strength asmaterial property values could not be actually obtained. As a result, itis not possible to quantitatively predict the adhesion reliability ofthe interface of resin-molded products, such that the adhering state andadhesion strength etc. of the interface should be actually tested andmeasured by actually making the resin-molded products.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor measuring adhesion strength of resin material which is capable ofseparating a true adhesion strength from a residual stress and ofaccurately and readily measuring a universal strength independent ofdimensions and shapes of specimens, and to provide a display method, acontainer and a carrying document of the resin material, using themeasured result and a manufacturing method of a composite body using themeasured result.

It is another object of this invention to provide a resin material theadhesion reliability of which at its product interface can be readilypredicted and evaluated from given material property values.

The first object can be attained by: making an adhering specimen havinga partial delaminating portion between a resin material and an adherendrequiring the adhesion strength and having a configuration as residualstress on the adhering interface near the delamination tip is dominatedby shear stress component; applying loads such that two types of shearstress in the positive and negative directions are generated on theinterface near the delamination tip; and obtaining apparent delaminationpropagating strengths in respective directions.

The second object can be attained by attaching the measured result ofthe adhesion strength obtained by the afore-mentioned means to the resinmaterial.

The display method, the container and the carrying document for theresin material according to this invention feature to describe anadhesion strength based on shear stress of a resin against an adherendmaterial together with the name of the adherend material, or to describean adhesion strength of the resin against the adherend material bysubstantially excluding influences of residual stress.

In this case, the term "resin material" represents a resin materialbefore being molded, and particularly in thermosetting resin itsignifies a resin composition. Further, the term "resin" represents acured product. The description is preferably made using a stressintensity factor or a strain energy release rate.

The stress intensity factor is typically represented in a unit of MPa √mor kgf/mm^(3/2), with dimensions of [(stress)×(length)⁰.5 ],[(force)×(length)⁻¹.5 ], or [(mass)×(length)⁻⁰.5 ×(time)⁻² ].

The strain energy release rate is typically represented by a unit ofJ/m² or kgf/mm, with dimensions of [(energy)×(length)⁻² ],[(force)×(length)¹ ], or [(mass)×(time)² ].

The method for measuring adhesion strength of resin material accordingto this invention features to comprise the steps of: forming adelamination portion between mutually adhered two materials; applyingtwo types of loads respectively such that opposed shear stresses aregenerated to the adhering interface; obtaining a delaminationpropagating strength for each load, or adhering in layers two materialsto be measured for adhesion strength; applying bending loadsperpendicular to the adhering interface by inverting their directionssuch that opposed shear stresses are generated, or generating stressesin the same and opposed directions as and to that of the residual stressacting on the adhering interface to obtain the adhesion strength.

Thus, according to the present invention, since the adhesion strengthsare obtained on the basis of the opposed shear stresses, the influencesof the residual stress can be offset.

The method for manufacturing a composite body according to the presentinvention features to select a combination of a resin and a metal forforming the composite body on the basis of an adhesion strength of theresin obtained when the metal is used as an adherend material.

In this case, the resin is epoxy, and the metal is preferably selectedfrom a group of copper, copper alloy, iron, aluminum or alloys thereofsuch as Fe-42 nickel etc. However, the resin is not limited to epoxy,but any thermoplastic resin or thermosetting resin can be used insteadthereof. Further, it does not matter whether the resin material isliquid or powder and whether the curing is made by heat or any otherfactor. The adherend material is not limited to metal, but also may beceramics or resin. Any form of cured product such as film, plate-typematerial or bulk may be used.

As the resin, thermosetting resins such as epoxy resin, silicone resin,and phenol resin, and thermoplastic resins such as polyethylene resin,polyamide resin are used. The resin may contain additives. Further,adhesives can be used as the resin e.g.: thermosetting resins such asepoxy resin basis; thermoplastic resins such as vinyl acetate-type resinbasis; elastomers such as chloroprene basis; and mix-type resins such asphenol resin-epoxy resin and the like.

Furthermore, the strength display according to the present invention isadvantageous particularly when applied to a composite body requiring tohave a certain adhesiveness of resin to a metal, so as to be apt toelectronic components such as resin encapsulated semi-conductor devices,power equipments such as resin insulating transformer, and domesticelectric appliances such as VTR chassis etc.

In this specification, the term "delamination propagating strength"stands for a strength against a propagation of a delamination from apreviously delaminated portion as an onset point.

The display can be made together with other conditions.

By generating two types of i.e. forward and backward (positive andnegative) shear stresses, it is possible to obtain two values ofdelamination propagating strength in two directions in that the residualstress increases and decreases the stress due to the load application.The apparent stress distribution near the delamination tip generatedonly by the load application can be accurately calculated from thedimensions, shapes and material properties of the specimen. Therefore,it is possible to obtain a universal true adhesion strength byarithmetically averaging these two values of apparent strength.

Namely, there is always any residual stress in an adhered product.Accordingly, in a measurement with a shear stress on the interface inthe direction opposed to that of the residual stress, "truestrength+residual stress" is measured. Meanwhile, in a measurement witha shear stress in the same direction as that of the residual stress,"true strength-residual stress" is measured. As a result, an average ofthese two resulting values, i.e. {(true strength+residual stress)+(truestrength-residual stress)}/2 would obviously represent the truestrength. These principles are found by the present inventors.

Moreover, for resin materials, if such measured results of the adhesionstrength are given, it would be possible to quantitatively predict andevaluate the adhesion reliability of molded products by analyzing stressoccurring in molded state on the basis of conventionally used materialproperty values such as Young's modulus and coefficient of linearexpansion, and comparing thus obtained stress to the adhesion strength.

The above and other advantages, features and additional objects of thisinvention will be manifest to those versed in the art upon makingreference to the following detailed description and the accompanyingdrawings in which a structural embodiment incorporating the principlesof this invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are front views showing a shape of a specimen and a loadapplying method in a method for measuring adhesion strength of resinmaterials according to an embodiment of the present invention;

FIGS. 2A and 2B are schematic views showing relationships betweenstresses when delamination propagation starts;

FIG. 3 is an explanatory view showing stress distributions near adelamination tip at a delamination propagating onset analyzed by finiteelement method in an adhering specimen of semiconductor encapsulatingepoxy resin to a semiconductor lead frame Fe-42 Ni alloy plate;

FIG. 4 is an explanatory view showing, in the same specimen as in FIG.3, relationships between apparent stress distributions generated only byload application, thermal stress distribution, and a critical stressdistribution as a true adhesion strength;

FIG. 5 is an explanatory view showing, in the same specimen as in FIG.3, relationships between apparent stress intensity factors generatedonly by load application, a stress intensity factor only by a thermalstress, and a critical stress intensity factor as a true adhesionstrength;

FIG. 6 is a front view showing a configuration of a specimen and a loadapplying manner in a method for measuring adhesion strength of resinmaterial according to a second embodiment of the present invention;

FIG. 7 is a front view showing a configuration of a specimen and a loadapplying manner in a method for measuring adhesion strength of resinmaterial according to a third embodiment of the present invention;

FIGS. 8A and 8B are front views showing a configuration of a specimenand load applying manners in a method for measuring adhesion strength ofresin material according to a fourth embodiment of the presentinvention;

FIG. 9 is a plan view showing a document carrying properties of a resinmaterial containing a measured result of adhesion strength according tothe present invention;

FIG. 10 is graphic view showing temperature dependence of true adhesionstrength of a semiconductor encapsulating epoxy resin to a semiconductorlead frame Fe-42 Ni alloy plate.

FIG. 11 is a cross-sectional view showing a resin-sealed typesemiconductor device in which a delamination generating temperature atthe interface is predicted from the adhesion strength, according to thepresent invention; and

FIG. 12 is an explanatory graphic diagram showing predicted delaminationgenerating temperatures in the resin-sealed type semiconductor deviceshown in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings.

FIGS. 1A and 1B are front views showing a shape of a specimen and loadapplying methods in a method for measuring adhesion strength of resinmaterials according to an embodiment of the present invention.

A strip-type or square specimen 1 has a two-layer structure in which aresin 2 is adhered to an adherend 3. An end of the adhering interface 4is previously provided with a delaminating portion 5. Such a type ofspecimen, which is subject to a bending load, is generally called ENF(End-Notched Flexure) specimen.

The resin material used in this embodiment is an epoxy resin compositionthat contains: cresol novolac epoxy resin as a main component; phenolnovolac resin as a curing agent; fused silica as a filler; and a smallamount of a plasticizer, a curing accelerator, a coupling agent, a moldrelease agent, a flame retarder, and a coloring agent.

For manufacturing the specimen 1, an adherend 3 is previously put in amold die, and the resin 2 is molded at a high temperature and then curedand thereafter cooled to a room temperature, or heated or cooled to testtemperatures.

Accordingly, residual stress τ_(r) is generated, mainly consisting ofthe shear stress component, due to cure shrinkage of the resin 2 anddifference in coefficients of linear expansion between the resin 2 andthe adherend 3. FIGS. 1A and 1B show acting directions of the residualstress τ_(r) near the delamination tip 7 in the case of the shrinkage orcontraction of the resin 2 being larger than that of the adherend 3.

Adhesion strength tests were carried out by executing three-pointsbending tests for both cases of upwardly and downwardly inverting thespecimen as shown in FIGS. 1A and 1B respectively, and measuring loadswhen the delamination propagation starts. Namely, in FIGS. 1A and 1B,the specimen 1 is supported by two supports 6 with the resin 2 sidebeing set to the upper side, and a load P₁ is applied to the center ofthe span. In FIG. 1B, on the contrary, the adherend 3 side is set to theupper side, and in the same manner a load P₂ is applied.

As a result, near the delamination tip 7 of the adhering interface 4,shear stress τ₁ generated by the load P₁ and shear stress τ₂ generatedby the load P₂ act in the directions as shown in FIGS. 1A and 1Brespectively.

Schematic representation of the relationships between the stresses whenthe propagation of delamination starts in the case of FIGS. 1A and 1Bare shown in FIGS. 2A and 2B.

In both cases of FIGS. 2A and 2B, the absolute value of the residualstress τ_(r) is identical, and the sign (positive or negative) isinverted only by an inversion of the coordinates. In FIG. 2A, when theload P₁ is applied, the shear stress τ₁ generated by the load P₁ firstlyreduces the residual stress τ_(r) and then inverts the sign, such thatthe propagation of the delamination starts upon the sum of both stressesτ_(r) and τ₁ reaches a critical shear stress τ_(c) as a true adhesionstrength.

On the other hand, in the case of FIG. 2B, the shear stress τ₂ generatedby the load P₂ acts to further increase the residual stress τ_(r), suchthat the summed stress reaches the critical stress τ_(c) with the loadP₂ being smaller than the load P₁ in the case of FIG. 2A, and then thedelamination starts.

In FIGS. 1A, 1B and 2A, 2B, the specimen 1 is upwardly and downwardlyinverted with the identical applying direction of the loads P₁ and P₂.Meanwhile, if it is supposed that the load applying direction isinverted while coordinates are defined with the specimen 1 as areference, the residual stress τ_(r) would be in the identical directionwhile the shear stresses τ₁, τ₂ generated by the loads are in theopposed directions for both FIGS. 1A, 2A and FIGS. 1B, 2B.

FIG. 3 shows a result of stress distribution, analyzed by finite elementmethod, near the delamination tip 7 along the adhering interface at anonset load of the delamination propagation which is measured when theload P₁ is applied from the resin 2 side as shown in FIG. 1A, for aspecimen consisting of semiconductor encapsulating epoxy resin adheredto a semiconductor lead frame Fe-42 Ni alloy plate.

Fe-42 Ni alloy has a very small coefficient of linear expansion incomparison with a general resin material so as to have a large residualstress when used to make a specimen. Conventionally, it has been aparticularly difficult material for the quantitative measurement ofadhesion strength with resin material.

The dimensions of the specimen are: 55 mm of length; 6 mm of width; 1.5mm of the resin thickness and 0.25 mm of the Fe-42 Ni alloy platethickness; 45 mm of distance between the supports for 3-points bendingtest; and 10 mm of distance from a support at the delaminating portionside to the delamination tip. Such specimens having been molded at 175°C. and then cured are tested at room temperature.

The stress analysis was carried out taking account of both the thermalstress and the load application on the assumption that the residualstress is generated by cooling from the molding temperature to the roomtemperature.

FIG. 3 shows, with x-axis in the direction parallel to the interface 4and y-axis in the direction perpendicular thereto as coordinates systemfor the specimen 1, distributions of normal stress σ_(y) and shearstress τ_(xy) which are two stress components relating to thepropagation of the delamination.

As shown in FIG. 3, near the delamination tip 7, the shear stress τ_(xy)is significantly larger than the normal stress σ_(y), and it isunderstood that the propagation of the delamination largely depends onthe shear stress component in the measuring method according to thisembodiment.

FIG. 4 shows an analyzed result of distribution of apparent shearstresses τ₁, τ₂ generated near the delamination tip by only thedelamination propagation onset load measured with respect to two typesof load applications shown in FIGS. 1A and 1B for the same specimen asin FIG. 3, and distribution of the shear stress τ_(r) generated by onlythe thermal stress, by use of finite element method.

Also, FIG. 4 shows a distribution of (τ₁ +τ₂)/2 and (τ₁ -τ₂)/2, anddistribution of the critical stress τ_(c) at the onset of delaminationpropagation equivalent to τ_(xy) in FIG. 3. As can be seen from FIG. 4,the arithmetic average (τ₁ +τ₂)/2 of the apparent shear stresses τ₁ andτ₂ generated by only the load application agrees well with the criticalstress τ_(c) at the onset of delamination propagation, while (τ₁ -τ₂)/2agrees with the shear stress τ_(r) generated only by the thermal stress.

Accordingly, it is possible to separate the critical shear stress τ_(c)as the true adhesion strength from the residual stress τ_(r) bycalculating the apparent shear stresses τ₁ and τ₂ for both cases ofinverting upwardly and downwardly the specimen 1 as shown in FIGS. 1Aand 1B.

The distribution of the critical shear stress τ_(c) obtained asaforementioned is not a single value so as to be improper to be directlyused as the true adhesion strength. Therefore, as a parameterrepresenting the stress distribution at the delamination tip as shown inFIG. 3, fracture mechanics parameters such as stress intensity factorand strain energy release rate are used.

The stress distribution on the interface near the delamination tip canbe expressed by use of the stress intensity factors K_(I) and K_(II) foropening-type (mode I) and in-plane shear-type (mode II) deformation, asfollows: ##EQU1## where σ_(y) : normal stress

τ_(xy) : shear stress

r : distance from delamination tip

π: number π

i : imaginary unit

d : representative length

The characters μ and υ represent the shear modulus and Poisson's ratiorespectively. The resin and the adherend are mutually distinguished bysubscripts p and a respectively.

As shown in the equation (1), the critical stress distributionequivalent to the true adhesion strength can be expressed by combiningtwo parameters K_(I) and K_(II).

In the case of interface formed of different kinds of materials, unlikein the case of the cracks in homogeneous materials K_(I) and K_(II) donot correspond to σ_(y) and τ_(xy) respectively, as represented by theequation (1). Therefore, both of these values cannot be separatelyconsidered.

So even when the shear stress component is dominant as in thisembodiment, the stress distribution cannot be represented only byK_(II), such that a combination of K_(I) and K_(II) should be used.

As a method for representing the stress distribution near thedelamination tip by a single parameter, it has been known a method usinga stress intensity factor K_(i) expressed by an equation noted below fora case of the residual stress being absent. This is disclosed in athesis in the Proceedings of the 67th Spring Annual Meeting of the JapanSociety of Mechanical Engineers previously noted. ##EQU2##

This parameter can be also applied to the separation of the trueadhesion strength from the residual stress previously mentioned, and iscapable of being easily calculated and evaluated in comparison with thecase using the combination of K_(I) and K_(II).

Namely, since there is a relationship of τ_(xy) >>σ_(y) as shown in FIG.3, K_(i) can be represented as the following equation (5) so as tocorrespond to the distribution of the shear stress τ_(xy) one to one.##EQU3##

When the specimen is vertically inverted as shown in FIGS. 1A and 1B torender the apparent K_(i) only by the applied loads P₁ and P₂(hereinafter referred to as K_(i1) and K_(i2)), it is possible tocalculate K_(i) corresponding to the true adhesion strength (hereinafterrepresented by K_(ic)) from their arithmetic average (K_(i1) +K_(i2))/2,and K_(i) corresponding to the residual stress (hereinafter representedby K_(ir)) from (K_(i1) -K_(i2))/2, such that the adhesion strength canbe evaluated from a single value.

K_(i) value for a desired load condition may be calculated on the basisof the stress distribution on the interface or the displacementdistribution on the delamination surface near the delamination tipanalyzed by numerical analysis such as finite element method or boundaryelement method. The calculating method is disclosed in the Transactionsof the Japan Society of Mechanical Engineers, Ser. A, Vol. 55, No. 510(1989) pp. 340-347.

K_(i) value for the load application in the embodiment shown in FIGS. 1Aand 1B may also be readily calculated using beam theory, withoutexecuting the numerical analysis, in the same manner as in the case ofthe strain energy release rate mentioned later.

FIG. 5 shows calculated results of: apparent stress intensity factorsK_(i1), K_(i2) only by the load application; stress intensity factorK_(ir) only by the thermal stress; and stress intensity factor K_(ic)corresponding to the critical stress when the propagation of thedelamination starts, taking account of both the load and the thermalstress.

Although there are somewhat large numerical analysis errors just nearthe delamination tip in other regions all the stress intensity factorsare substantially constant.

As shown in FIG. 5, it is understood that the values (K_(i1) +K_(i2))/2and (K_(i1) -K_(i2))/2 agree well with the stress intensity factorsK_(ic) and K_(ir) corresponding to the true adhesion strength and theresidual stress, respectively.

In this embodiment, the residual stress and the true adhesion strengthare obtained by thermal stress analysis. For certain types of resinmaterials, however, it is sometimes necessary to measure, in advance ofthe analysis, detailed temperature-dependent data of properties such ascoefficient of thermal expansion or Young's modulus corresponding to athermal history from the specimen molding to the adhesion strength test,due to the conspicuous temperature dependency of the materialproperties. In another case, further, significant viscoelastic behaviorof the material at high temperatures would sometimes make the analysisvery complicated or make accurate residual stress analysis difficult.

According to this embodiment where the residual stress is separated andeliminated only by using the apparent K_(i) 's with respect to the loadapplication, the true adhesion strength can be readily and accuratelyobtained without analyzing the residual stress.

Further, since the stress intensity factor K_(i) can uniquely representthe intensity of the stress near the delamination tip, a universaladhesion strength independent of the dimensions and shapes of thespecimen can be obtained.

The K_(i) value for the load application in the embodiment shown inFIGS. 1A and 1B can be derived using beam theory in the followingmanner. Namely, the deflection at the loading point when a load P isapplied to the center between the supports 6 can be represented as thefollowing equation (6), wherein: b, width of the specimen 1; t_(p),thickness of the resin 2; t_(a), thickness of the adherend 3; 2L,distance between the supports in three-point bending; a, distance fromthe support 6 at the side of the delaminating portion 5 to thedelamination tip 7; E_(p), Young's modulus of the resin 2; E_(a),Young's modulus of the adherend 3. ##EQU4##

Since the compliance C for the load P is expressed as δ/P, the strainenergy release rate G can be obtained as follows: ##EQU5##

There is a following relationship between the stress intensity factorK_(i) and the strain energy release rate G: ##EQU6##

Accordingly, the stress intensity factor K_(i) can be easilyarithmetically calculated from the equations (7) and (8).

There is a following relationship between the Young's modulus E, theshear modulus μ, and the Poisson's ratio υ. For the calculation, two ofthese three should be previously calculated. ##EQU7##

The material property values necessary for the analysis of the apparentstress or the stress intensity factor generated only by the load areonly these values of material properties at the test temperatureregardless of the thermal-history from the molding temperature etc.

The aforementioned strain energy release rate G can also be used as aparameter representing the true adhesion strength-instead of the stressintensity factor K_(i).

In this case, the strain energy release rate G is proportional to asquare of the stress intensity factor K_(i) and that of the stress. Forcalculating the strain energy release rate G_(c), G_(r) corresponding tothe true adhesion strength and the residual stress from the apparentstrain energy release rate G₁, G₂ for the loads P₁ and P₂, it isnecessary to execute the following additional and subtractivecalculations for the square roots: ##EQU8##

For representing the true adhesion strength, in addition to theaforementioned stress intensity factor K_(I), K_(III), the stressintensity factor K_(i), and the strain energy release rate G, any otherparameters capable of uniquely representing the intensity of the stressnear the delamination tip regardless of the dimensions and shapes of thespecimen, such as path-independent integral J used in fracture mechanicscan be used.

In practice, it is also possible to use values of the delaminationpropagation onset loads from opposed directions, or a value of theaveraged delamination propagation onset load of the opposed loads withthe same delamination distance in a condition of a predetermineddimension and shape of the specimen.

These load values can also be converted into desired universalparameters, if necessary.

Any of the thermosetting and thermoplastic resin materials can be usedfor the adhesion strength measurement. Further, it is possible to use asthe adherend material apart from the metal, inorganic materials such asceramics, silicon and glass etc., other resin materials, and the samebut separately formed resin material. Residual stresses other thanthermal stress caused by any reason such as shrinkage at the curingreaction, swelling due to permeation of water or chemical liquid etc.,and material alteration due to physical or chemical environmentalfactors and the like can also be separated.

On determination of the dimensions of the specimen 1, the followingconditions should be satisfied:

(1) The interface 4 is not delaminated by the residual stress at thestage of making the specimen 1;

(2) The resin 2 and the adherend 3 are not fractured or plasticallydeformed in advance of the delamination of the interface;

(3) Any large deformation, which would be out of the application of beamtheory or linear numerical analysis does not take place at the bendingtest; and

(4) The influence of the shear stress acting in the width direction ofthe specimen 1 i.e. in the direction perpendicular to the page plane ofFIGS. 1A and 1B can be ignored.

For the condition (1) the resin 2 is preferably thinner as far aspossible than the length or the width of the specimen. Meanwhile, on thecontrary, for the conditions (2) and (3) the resin 2 should not bepreferably too thin compared to the distance between the supports inthree-points bending. For the condition (4), it is preferable to set thewidth of the specimen 1 to a sufficiently small value in comparison withthe distance between the supports.

The critical values of the dimensions satisfying the above conditionsdepend on the combination of the kinds of the resin 2 and the adherend3, but it could be present the general measures as follows:

The thickness of the specimen is preferably in a range of 1/5-1/40 ofthe distance between the supports, and the width of the specimen ispreferably not exceeding 1/5 of the distance between the supports; and

The delamination tip 7 is preferably separated from both the support 6and the loading point by a distance equal to or more than the thicknessof the specimen.

To form the delaminating portion 5 at one end of the specimen 1 inadvance of the adhesion strength test in FIGS. 1A and 1B, a mold releaseagent is coated on one end of the adherend 3 before molding the specimen1, or a tape made of less adhesiveness material such as fluororesin isapplied thereon.

Without using such delaminating means before molding, also, it ispossible to form the delaminating portion by previously reducing thedistance between the supports 6 before the adhesion strength test andapplying a local bending load to near the end portion of the specimen 1,or pressing a razor blade to the end portion of the specimen 1.

Even in the case of using the delaminating means before molding, it ispreferable to further propagate a natural delamination from the tip ofthe resulting delaminated portion by applying a bending load etc. inorder to enable more accurate measurement of the adhesion strengthwithout being disturbed by the applied tape etc.

The length of the delaminating portion 5 which is necessary to calculatethe stress intensity factor K_(i) and the like may be measured through amicroscope observation of the side surface of the specimen, or anultrasonic inspection from the upper or the lower surfaces. When thedelaminating means is used before molding the specimen, it is alsopossible to measure the coated length of the mold release agent or theapplied length of the tape. But the latter case is premised on that thedelamination is not propagated after the molding.

The onset of the propagation of the delamination in the three-pointsbending test can be detected by a change in the compliance C due to thechange in the delamination length, i.e. a folding of a curverepresenting the relationship between the load P and the deflection δ.Alternatively, it is also possible to detect acoustic signals generatingupon the onset of delamination propagation through an acoustic emissiondetector or a microphone etc.

In the aforementioned example, the adhesion strength has been obtainedbased on the propagation onset of the delamination. However, in certainmaterials, the stress intensity factor K_(i) and the like sometimes varydepending on the states of the propagation such as propagation onsettime, during the propagation, propagation stopping time. In such a case,the stress intensity factor value at a proper time point may be used inaccordance with the use of the required adhesion strength.

FIGS. 6 and 7 are front views showing a configuration of the specimenand a load applying manner respectively, in a method for measuringadhesion strength of resin material according to further embodiment ofthe present invention.

The specimen used in the present method need not be composed of only twomaterials, the resin 2 and the adherend 3 being the medium for themutual adhesion strength test. For example, as shown in FIG. 6, it isalso possible to measure an adhesion strength of the resin 2 heldbetween the same or different two adherend 3a and 3b at the interface 4of the material 3a side or to measure an adhesion strength of the resin2 to the second adherend 3a formed on the surface of the first adherend3b by plating, adhesion or deposition or the like as shown in FIG. 7.

Moreover, not limited to such two-layer and three-layer structures asshown in FIGS. 1A and 1B, 6 and 7, it is also possible to use amultilayered structure with equal to or more than four layers, or astructure that a particular material is present only in a part of theentire length of the specimen. In these cases, the delaminating portion5 should be formed at the interface 4 between the materials to be servedfor the adhesion strength measurement.

In FIGS. 6 and 7, the load applying manner for applying the load P₁ onlyfrom one direction respectively is shown. However, in the same manner asin the case of the embodiment shown in FIGS. 1A and 1B, the three-pointsbending test is carried out for both cases of inverting the specimenupwardly and downwardly and the true adhesion strength is separated fromthe residual stress.

FIGS. 8A and 8B are front views showing a configuration of the specimenand load applying manners in a further different embodiment of thisinvention.

In this embodiment, a compressive load P₁ as shown in FIG. 8A and atensile load P₂ as shown in FIG. 8B are applied in the directionparallel to the interface 4 of the specimen composed of mutually adheredresin 2 and the adherend 3 to generate mutually inverted shear stressesτ₁ and τ₂.

Thus, according to this embodiment, specimens of any configuration andany load applying manner may be used so long as the shear stresses nearthe delamination tip 7 can be mutually inverted and the shear stressescan be set to a value sufficiently larger than that of the normal stressgenerating perpendicularly to the interface 4.

When the compressive and tensile loads are applied as shown in FIGS. 8Aand 8B, for reducing the normal stress component, the loads to beapplied at both ends of the specimen 1 in the opposed directions shouldbe on a single axial line and the specimen 1 should not be subject tothe bending moment.

When the adhesion strength test is executed by bending load, apart fromthe three-points bending load method shown in FIGS. 1A and 1B etc., avariety of load applying manners such as four-points bending loadmethod, or a method of applying a bending load to a cantilever-supportedspecimen and the like. In these cases, the stress intensity factor K_(i)and the strain energy release rate G are calculated through beam theory.

FIG. 9 is an example of a document carrying properties of the resinmaterial as a result of the adhesion strength measurement according tothe present invention.

If material property values such as conventionally used Young's modulusor bending elastic modulus instead thereof, Poisson's ratio andcoefficient of linear expansion etc. for both the resin material and theadherend material are measured or given, the stress generating on theadhering interface inside a completed resin molded product etc. can bepredicted by analysis.

Accordingly, if the true adhesion strength represented by parameterssuch as K_(i) obtained through the present method is given in the formof the document shown in FIG. 9, it is possible to quantitativelypredict and evaluate the presence/absence of the delamination at theinterface and the degree of the delamination by comparing the adhesionstrength and the predicted result of the stress, without need ofactually making a completed product of the resin material.

In the present invention, the adhesion strength against the delaminationpropagation in case of already existing the delaminating portion isobtained. Therefore, for predicting the presence/absence of thedelamination within a product on the basis of the above adhesionstrength, presence of a small delaminating portion is supposed, andpresence/absence of the propagation of the delamination therefrom isevaluated.

While the conventional adhesion strength could be used only for relativecomparison between materials because of its dependency on the dimensionsand configuration of the specimen, the adhesion strength measured by thepresent method can be applied to the quantitative evaluation of theadhesion reliability of molded product. Therefore, for describing themeasured result, the measuring method such as a method usingthree-points bending test by upward and downward inversion or a methodusing inversion of shear stress may be preferably noted.

The measured result of the adhesion strength may be also described, inaddition to the test records as shown in FIG. 9, on a variety ofspecifications of the resin material and on the container, so as toenable the prediction and the evaluation of the adhesion reliability ofthe resin material.

As aforementioned, Poisson's ratio of the resin is necessary for theanalysis of the generating stress. But since it is more complicated tomeasure the Poisson's ratio compared to the bending elastic modulus orthe like and this ratio has an insignificant influence on the stressanalysis result, the description of Poisson's ratio may be omitted fromdescription as in the example shown in FIG. 9.

The adhesion strength of the resin varies depending on the kind or thesurface state of the adherend, environmental conditions such astemperature and humidity, and molding conditions. Therefore, themeasured results of the adhesion strength may preferably be noted innumerical values together with the such conditions, or represented inthe form of graphs with respect to such conditions as temperatures etc.

FIG. 10 is a graphic diagram showing temperature dependence of trueadhesion strength K_(i) of semiconductor encapsulating epoxy resin to asemiconductor lead frame Fe-42 Ni alloy plate obtained according to thepresent invention.

In the conventional method for measuring adhesion strength, thetemperature dependency of the adhesion strength could not bequantitatively calculated since not only the true adhesion strength butalso the residual stress changed in accordance with the temperature.According to the present invention, meanwhile, if the true adhesionstrength is given in the form of a function of temperature, the criticaltemperature of the delamination generation can be predicted by beingcompared to the generating stress of the molded product calculated bythe analysis as the function of temperature.

According to the present invention, two kinds of adhesion strength, i.e.when the residual stress is added to and subtracted from the stresscaused by the load application can be provided and the stressdistribution at the interface can be taken account. In consequence, thetrue adhesion strength can be separated from the residual stress withoutexecuting any analysis of the residual stress, and universal adhesionstrength can be accurately and readily measured independently from thedimensions and configuration of the specimen.

Furthermore, in this invention, since the stress of the product obtainedthrough analysis and the true adhesion strength can be compared, thereliability of the interface inside the molded product can be predictedand evaluated without actually making the molding product.

Next, there will now be shown an example where a delamination generatingtemperature, at an adhering interface between a lead frame and a sealingresin when a resin-sealed type semiconductor device is heated, ispredicted from an adhesion strength, according to this invention.

In FIG. 11, a semiconductor element 8 is fixed to a tab 9 portion of aFe-42 Ni alloy lead frame by adhesive agent or the like. A plurality ofleads 10, made of the same material, are formed around the tab 9. Theelectrode and the leads 10 are mutually in electrical connection throughfine metal lines not shown. These components are molded by epoxy sealingresin 11, except external coupling portions of the leads 10.

Such a resin-sealed type semiconductor device as shown in FIG. 11 isexposed to a high temperature of equal to or more than 200° C. whenmounted on a wiring substrate by soldering. Thermal stress generating atthis time would cause delamination at interfaces in the semiconductordevice. In order to evaluate the delimination criteria, it is useful toapply the stress intensity factor K_(i) at the delamination tip.Therefore, a small delaminating portion 12 is assumed at an end portionof an adhering interface between the sealing resin 11 and the lowersurface of the tab 9. Values of the stress intensity factor K_(i)generating at the delamination tip 13 when the resin-sealed typesemiconductor is heated at a variety of temperature are analyzed usingfinite element method. Further, true adhesion strength value K_(ic) atvarious temperatures between the sealing resin 11 and the lead framematerial are measured so as to be compared to the aforementionedanalyzed value.

FIG. 12 shows the compared result. In FIG. 12, the increasing curve(left down-right up) represents an analyzed relationship between thegenerated stress intensity factor K₁ and the heating temperature, whilethe decreasing curve (left up-right down) represents an experimentallyobtained relationship between the true adhesion strength K_(ic) and themeasuring temperature. The intersecting point of both curves representsa generating temperature of the delaminating propagation. A variety ofmarks on the curve representing the analyzed stress intensity factorK_(i) in FIG. 12 show states of delaminating generation at the lowersurface of the tab 9 observed through an ultrasonic inspecting apparatusafter an actual resin-sealed type semiconductor device is put in anisothermal vessel for ten minutes. The white circle indicates a samplewithout showing any delamination at the lower surface of the tab 9 atthat temperature, the black circle indicates a sample with a totaldelamination of the lower surface of the tab 9 at that temperature. And,the white-black mixed circles indicate partial delamination of theportions near the end of the lower surface of the tab 9, in which thesize of the delamination is represented by way of the ratio of the blackregion to the white region in the circle.

As can be seen from FIG. 12, no delamination is observed at temperatureregions where the generated stress intensity factor K_(i) is less thanthe true adhesion strength K_(ic), a total delamination is observed attemperature regions where K_(i) is higher than the true adhesionstrength K_(ic), and partial delamination is observed at temperatureregions near the intersecting point of both curves. These resultsindicate that the generation of the delamination inside the resin-sealedsemiconductor device can be predicted by comparison of the adhesionstrength obtained according to this invention with the analyzed stressintensity factor of the resin-sealed type semiconductor device.

If the generation of the delamination can be quantitatively predicted asmentioned above, it is possible to select optimum resin material, leadframe material, surface treating conditions e.g. plating for the leadframe, resin molding conditions and conditions for combining thereof,without actually making molded products of the resin material.

What is claimed is:
 1. A method for determining an adhesion strength ofa resin material in a structure having two or more kinds of materialsincluding at least one resin material, comprising steps of:forming adelamination portion at an adhering interface between said at least oneresin material and another material adhered to said at least one resinmaterial; applying two types of loads respectively such that opposedshear stresses are generated to the adhering interface; and obtaining adelamination propagating strength for each of the two types of loads. 2.A method according to claim 1, wherein said two types of loads areapplied such that stresses are produced in the same and opposeddirections as and to a direction of a residual stress acting on theadhering interface.
 3. A method according to claim 1, whereinsaid two ormore kinds of materials are laminated; and said two types of loadscomprise bending loads perpendicular to the adhering interface byinverting a direction of one of the two types of bending loads against adirection of another of the two types of bending loads.
 4. A methodaccording to claim 1, whereinsaid two or more kinds of materials arelaminated; and said two types of loads are composed by respectivelyapplying stresses in the same and opposed directions as and to adirection of the residual stress acting on the adhering interface.
 5. Amethod according to claim 4, wherein said two types of loads arecompressive and tensile loads.